Generally, a wireless communication system uses electromagnetic waves to communicate with a fixed/mobile wireless communication terminal (for example, a cell phone or a laptop attached with a wireless communication card can be called a terminal). Generally, the terminals are located within the wireless coverage range of the system, and electromagnetic wave frequencies allocated to these terminals are divided into a plurality of carrier frequencies to serve as wireless communication channels. The wireless communication system adopts specified wireless channels to provide wireless coverage range within a geographical range through a Base Station (BS), and the geographical range is called a cell. Generally, the BS is located in the center of the cell.
The coverage range of a wireless network would be affected by various factors. For example, a high building might block the radio signal of the BS, thereby causing serious weakening of the signal within a certain region, and the signal at the edge of the cell would be weakened, thereby causing increase of reception error rate of the terminal. The capacity requirement of the wireless communication system also is affected by various factors. For example, when the number of users increases rapidly or a call traffic increases rapidly, the system capacity is required to be increased; however, in a remote area, the capacity of a BS generally can not be fully utilized within the coverage range, thus it is needed to expand the coverage range of the system so as to make full use of the redundant system capacity.
In order to expand the system coverage range or increase the system capacity, one or more Relay Stations (RSs) can be set between a BS supporting multi-hop relay and a terminal (hereinafter the wireless communication system comprising an RS is called a system). The RS can be used to relay the signal from the BS to the terminal (downlink) or from the terminal to the BS (uplink). After the RS is adopted, the signal transmission quality of the communication link can be effectively improved, so as to achieve the purpose of expanding the system coverage range or increasing the system capacity.
The communication path, through which the terminal accesses the BS via one hop RS or multi-hop RSs, is called a relay path. The RS directly connected with the terminal is called an access RS. The communication link between the access RS and the terminal is called an access link. On the relay path, the access RS can communicate with the BS through other RSs. On the relay path, the communication link between RSs or between RS and BS is called a relay link. The RS can be fixed, roaming or mobile.
FIG. 1 shows schematic diagrams of a conventional data sending mode and a Local Forwarding mode in a multi-hop system according to relevant art. The data communication path of a conventional cellular network is as shown in FIG. 1 (a), no matter how far two communicated Mobile Stations (MS) are away from a BS and how poor the link quality is, the MSs must establish a connection with the BS directly and occupy the system resources (since the link quality is poor, the utilization efficiency of the resources is very low, a lot of resources might be occupied to guarantee the needed Quality of Service (QoS) to communicate). The data communication path of a Mobile Multi-hop Relay (MMR) cellular network is as shown in FIG. 1 (b), for the communication between the MSs which are far away from the BS or are under poor link quality, the forwarding of an RS enables a single-hop path BS<->MS with poor link quality to be replaced by a two-hop link, MR-BS<->RS and RS<->MS, with good link quality, thus a high-order Modulate Code format Set (MCS) can be used to improve the utilization efficiency of the resources and to obtain a higher throughput performance. However, for two intercommunicated MSs, no matter how close they are, they must adopt the forwarding of the RS to transmit data to the MR-BS so as to perform communication. For the MS1 and the MS2 accessing the same RS, after the data of the MS1/MS2 are forwarded to the MR-BS by the RS, the MR-BS transmits the data back to the RS again, and then the RS transmits the data to the MS2/MS1, that is to say, the same data are forwarded back to the RS from the MR-BS after being forwarded to the MR-BS by the RS, thus unnecessary air interface overhead is caused and the utilization efficiency of the spectrum resources of the network is reduced. FIG. 1 (c) shows a data communication path in a Local Forwarding mode, the MSs in the same RS can intercommunicate directly through the forwarding of the RS, without forwarding data to the MR-BS, thus the air interface resources of the MR-BS are saved.
Since a user, when entering network, performing a secondary route selection and a handover, needs to select a proper cell, a proper sector and a proper station to perform access, so as to satisfy the QoS requirement of the user itself, a necessary path selection algorithm can maximize the resource utilization efficiency and the system capacity to satisfy the growing service requirement of the user on the premise of guaranteeing the QoS of the user.
For example, a newly joined MS must perform an action of Network Entry with an adjacent higher-level station to join the network, wherein this higher-level station can be an MR-BS, also can be an RS. When performing the action of Network Entry, the MS would monitor a Preamble of the higher-level station, synchronize with the higher-level station, and then perform an action of Initial Ranging. Generally, during the phase of the MS performing the action of Initial Ranging, the MS would select the adjacent station with strongest signal intensity to perform interaction; after a series of actions such as signal intensity adjustment, parameter setting and registration authentication are completed, the MS can join the network formally. Therefore, the MS accomplishing the action of Network Entry can communicate with the MR-BS.
FIG. 2 shows a schematic diagram for illustrating a control channel and a data channel in a Local Forwarding mode according to relevant art. As shown in FIG. 2, if the Local Forwarding technology is adopted, the signaling system still adopts the original non-shortcut mode, a series of signaling interaction comprising traffic statistic and charging information still would pass through the MR-BS, the operator still can fully monitor the network according to its own desire, in this way, the redesign of the signaling system due to the introduction of a novel technology is simplified, the Local Forwarding technology can be used with few changes. However, in order to improve the spectrum efficiency of the system, the data service adopts the shortcut mode to transmit, no longer being necessary to pass through the MR-BS.
Although the MS can determine the connected higher-level station by judging the signal intensity, however, only using the signal intensity as the criteria of route selection might not select a better path. It is necessary for us to take the resource utilization efficiency and the service condition of the user into account during the secondary route selection and the handover and make them the route selection criteria, so as to optimize the path selected by the user and make full use of the advantages of the Local Forwarding.
Before introducing a detailed routing algorithm, a timeslot utilization efficiency is first defined which is used to represent the link efficiency of each hop of link (a single-hop link or a relay link and an access link on a multi-hop path) on each optional path.
In the Institute for Electrical and Electronic Engineers (IEEE) 802.16 standard, a slot is the smallest time-frequency resource allocation unit in the system, and the resources that each user can obtain are an integer multiple of slots. According to the definition of the standard, in a 10 MHz-bandwidth 1024-Fast Fourier Transform Algorithm method (FFT) system, one slot comprises 48 data sub-carriers for transmitting data information of the user. The system adopts an adaptive modulation and coding technology, if a Signal Interference Noise Ratio (SINR) of the link can satisfy an MCS using M (M=2m)-level modulation, with a coding rate of r, then one data sub-carrier on this link can carry m×r (bit) information, then we define η(m,r,Tframe) as the slot utilization efficiency.
                              η          ⁡                      (                          m              ,              r              ,                              T                frame                                      )                          =                                            48              ×              m              ×              r                                      T              frame                                ⁢                      (                          Kbps              /              Slot                        )                                              (        1        )            
In the above, Tframe represents a frame length. The slot utilization efficiency actually represents a data rate that one slot can transmit.
Different MCSs correspond to different slot efficiencies, since different links have different link quality (SINR), and different SINR ranges correspond to different MCSs, thus formula (1) can also be expressed as follows:η(m,r,Tframe)=η(SINR)  (2)
The MCSs and the slot efficiency corresponding to different SINR ranges are shown in Table 0.
TABLE 0MCS Correspondence Table ListSINR(dB)Slot EfficiencyMCS(PED-B: 3 km/h)(Kbps/Slot)QPSK( 1/12)−3.141.6QPSK(⅙)−0.733.2QPSK(⅓)2.096.4QPSK(½)4.759.6QPSK(⅔)7.8612.816QAM(½)9.9419.216QAM(⅔)13.4525.664QAM(⅔)18.638.464QAM(⅚)24.5848.5
In the multi-hop relay cellular network, the MS can have multiple optional paths, and the MS can communicate with the BS directly, also can perform multi-hop communication through the forwarding of the RS. For a user u, provided there are np(u) optional paths between the user u and the MR-BS totally.
Pl(u) represents each optional path between the user u, and the MR-BS, wherein l=1, 2, . . . , np(u).
Provided there are hl(u) hops on the optional path Pl(u) between the user u and the MR-BS, Pli(u) is adopted to represent the ith hop of link on the path Pl(u), wherein i=1, 2, . . . hl(u).
SINRli(u) represents the SINR of the link Pli(u), then η(SINRli(u)) is the slot efficiency of the link Pli(u).
However, at present, an access station which establishes a route with the terminal can not be selected according to actual application conditions.